Chapter 8, Problem 8.83P

Given 0.603MW electrical power supplied to a boiler when the temperature of the entering water is 20 C and the exiting temperature is 89 C. The flow of.the pressured water is 2 Kg/s. There is a negligible pressure drop through this boiler and it operates at a constant pressure of 3 bars. The specific heat is c = 4,370 J/(Kg K).  a) Calculate the total rate of entropy production b) Calculate the total rate of exergy destruction (W). The dead state temperature is 293.2 K and pressure is 1 bar. c) Calculate the mass flowrate of fuel (natural gas, CH4) required to heat the water flow to the conditions of the problem if the electrical heating device is replaced with a gas fired boiler. The high heating value (HHV) of the fuel is 50.02 MJ/kg.

SU-2 A gas at 500K is in a cylinder with a frictionless piston. The gas goes thru a reversible cycle during which it absorbs 400J from a reservoir at 500K. During part of the cycle the gas rejects heat Q to a reseroir at 300K. Let the system be defined as the gas. a) What is the change in entropy for the system for one cycle of operation of the engine? Briefly explain your answer. b) Find the change in entropy for the universe for one cycle of operation of the engine. Briefly explain your answer. c) Find the change in entropy for the surroundings for one cycle of operation of the engine. Briefly explain your answer. d) Use your results from the previous parts to find how many joules of heat were rejected to the 300K reservoir during this process.

1. A closed tank, V = 10 L, containing 5 kg of water initially at 25 °C, is heated to 150 ° C by a heat pump that is receiving heat from the surroundings at 25 ° C. Assume that this process is reversible. Find the heat transfer to the water and its change in entropy.